Print actuation system employing magnetically actuatable hammers and movable type carrier

ABSTRACT

A print mechanism by which printable characters transported across a page may be printed by individually magnetically actuated hammers aligned along a print line. The actuation of the hammers is accomplished by banks of electrically driven solenoids wherein the solenoids in each bank are contained in a common magnet bar oriented angularly around the hammer pivot centers and providing a common magnetic return path for all of the solenoids in an associated bank and acting as beams for supporting the actuation forces of the solenoids.

United States Patent [72] Inventors Seymour M. DePuy;

John R. Bittner, Waynesboro, Va. [21] Appl. No. 734,498 [22] Filed June 4, I968 [45] Patented Feb. 23, 1971 [73] Assignee General Electric Company [54] PRINT ACTUATION SYSTEM EMPLOYING MAGNETICALLY ACTUATABLE HAMMERS AND MOVABLE TYPE CARRIER 13 Claims, 5 Drawing Figs.

[52] 11.5. C1 101/93 [51] Int. Cl B41] 1120, B4 1 j 9/38 [50] Field ofSearch 101/93, 93 (RC), 96,109,178(lnquired), 317,111

[56] References Cited UNITED STATES PATENTS 2,874,634 2/1959 Hense 101/93 2,936,704 5/1960 Hense 101/93 3,041,964 7/1962 Simpson et a1 101/111 3,051,785 8/1962 Harding,.lr 101/93X 3,077,830 2/1963 Paige 101/93 3,212,435 10/1965 Walker 101/93 3,306,191 2/1967 Sharples.... 101/93 3,308,749 3/1967 Dowd 101/93 3,416,442 12/1968 Brown et a1 101/93 Primary Examiner-William B. Penn Anameys Lawrence G. Norris, Michael M asnik, Stanley C,

Corwin, Frank L. Neuhauser, Oscar B. Waddell and Melvin M. Goldenberg ABSTRACT: A print mechanism by which printable characters transported across a page may be printed by individually magnetically actuated hammers aligned along a print line. The actuation of the hammers is accomplished by banks of electrically driven solenoids wherein the solenoids in each bank are contained in a common magnet bar oriented angularly around the hammer pivot centers and providing a common magnetic return path for all of the solenoids in an associated bank and acting as beams for supporting the actuation forces of the solenoids.

PATENTEUFEB23|97| I $564,999

' sum 1 or 4 5 HAMMER DRlVE I CIRCUIT s;

THEIR ATTORNEY PATENTEB FEB23 1971 INVENTOR. M. DePUY BITTNER SEYMOUR JOHN BY g THEIR ATTORNEY SHEET 2 OF 4 PATENTED FEB23 19m SHEET 0F 4 llVVENTOR. OUR M. DePUY N R BITTNER SEYM JOH THEIR ATTORNEY BACKGROUND OF THE INVENTION This invention relates to an improved print mechanism by which printable characters transported across a page may be printed by means of magnetically actuated hammers aligned along a print line.

Printers of the type of which the present invention relates include a moving print carrier having a spaced row of print characters on the outer peripheral surface thereof. A plurality of hammers are individually actuable to engage the print characters and drive them against an inked ribbon and a record medium such as paper, disposed between the carrier and the ribbon and cause the characters on the carrier to print the desired information, line by line, on the paper. The hammers are solenoid-actuated and selective energization of the solenoids is coordinated with the drive mechanism for the print carrier in a manner to effect printing of the desired character from information received from a source such as a computer, remote terminal or tape reader, etc. For further details of one type of printer arrangement for which the present invention has application, reference can be made to US. application Ser. No. 734,501, filed Jun. 4, 1968 in the names of Clifford M. Jones and Earle B. McDowell and entitled Print Selection System."

While it is common practice to print from moving type by means of magnetically actuated hammers, in those machines having print hammers aligned along each print column space across the printed page, the close spacing of the hammers does not allow adequate room for the mounting of magnets having commensurate size and power to drive the hammers. Adequate magnet size is achieved by using the space both above and below the print line and by costly and intricate arrangements of the magnets. Problems arise in attempting to provide the desired degree of rigidity, while other problems exist with shielding the magnets to prevent interaction between the magnetic field of adjacent magnets. A need exists for a design to provide improved magnetic and structural utilization of the magnetic material to attain better magnet efficiency and to minimize leakage fields. A need also exists for an arrangement which optimizes transfer of energy from the traction or pulling magnet to the print hammer, improves visibility of the print line while permitting simplicity in assembly adjustment.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an improved actuation arrangement for 'print hammers in a printing mechanism.

It is a further object of this invention to provide an improved print mechanism construction yielding optimum performance with the minimum of costs.

It is a further object of this invention to provide a print hammer-actuating assembly of improved magnetic and structural performance.

It is a further object of this invention to provide an improved magnet bar arrangement which permits a common magnetic return path for all of solenoids incorporated in it and acts while also serving as a common beam to support the actuating forces of the solenoid.

It is a further object to provide an improved magnetic control arrangement.

Briefly, these objects and others are achieved according to one embodiment of the invention by providing a plurality of banks of electrically driven solenoids proving actuation for the print hammers. Individual-hammers at each of the print positions are mounted in a single hammer bar. Clevis assemblies connect each hammer to a solenoid plunger. Each bank of solenoids is mounted on a common magnetic bar in spacedapart relation. Tbe'individual magnet bars are oriented angularly around the hammer pivot centers and extend the length of the print line. Each magnet bar provides a common magnetic return path for all of the solenoids incorporated in it and acts as a beam to support the actuation forces of the solenoid. The solenoid plungers enter through holes in the top member of the magnetic bar. Aligned with the holes in the top member are threaded holes in the bottom of the magnetic bar which receive the pole pieces and by which, adjustment of the plunger travel is made. The magnet bars are mounted at their ends to pulley castings in the proper orientation.

BRIEF DESCRIPTION OF THE DRAWINGS The subject matter of the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. For a complete understanding of one embodiment of the invention together with other objects and advantages thereof, reference should be made to the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 shows a section view of the hammer and magnet bar assembly.

FIG. 2 is a schematic representation of hammer magnet connection and the offset positioning of the magnet bars.

FIG. 3 is a sectional detail of a magnetic bar illustrating the mounting of the solenoid and clevis assembly.

, FIG. 4 illustrates a detail of a hammer construction and the nature of the angular coupling to each magnet bar.

FIG. 5 combines the hammer drive and bar magnet arrange ment disclosed in the other drawings in a single isometric view.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. I, there is shown a portion of a rotatable print carrier 1 having circumferentially spaced rows of type characters on the outer periphery thereof. In a preferred embodiment as referenced in the earlier application, the characters are embossed on individual type elements 2 which occur at one end of respective flexible finger3. Fingers 3 .are made of resilient material and are mounted at their other ends in the carrier 1 which may be of belt construction. As the print fingers move along a line of type, they are driven into an inked ribbon 4 and a recording medium such as paper 5 supported by platen 6 by means of respective hammers 7. The plurality of such hammers is supported for rotation about a common pivot bar or shaft 8 carried by a respective hammer support bar 35 and is thereby aligned along a print line on the paper 5. Hammers 7 are actuated by individual solenoids 9 which are selectively energized in accordance with logic available from a control circuit 10. The details of the control circuit depend on the particular type of print communication involved.

In the arrangement of FIG. 1 and FIG. 5. the particular hammer shown mounted on the common pivot bar or shaft 8 is adapted for rotary motion about the pivot bar in response to energization of a particular solenoid 9', for example, the one shown as in the extreme left position of the drawing. This solenoid operates the hammer located in position A as contrasted with the other positions shown in greater detail in FIG. 4. Energization of the solenoid provides hammer movement by movement of its associated plunger 11 in a manner to be described shortly. This movement of the plunger is transmitted by means of the associated clevis assembly 12. Clevis assembly 12 is linked to the plunger at one end by clevis pin 13 and at it other end engages the curved clevis slot of the hammer by pin 14. Each hammer 7 is normally biased against hammer stop 15 by a respective spring 16. Action of the plunger in a direction away from the clevis assembly 12 imparts angular motion to hammer 7 causing it .to be driven into the type finger 2 and produce printing as previously described. Since the action of the solenoid energization is brief, the hammer after completing its travel is-returned to its hammer stop position by means of spring 16. This arrangement of FIG. 1 wherein the magnets are connected to the hammer by means of clevis links which are pinned to the magnet plungers and engaged slotted extensions on the hammers results in improved operation. The slots permit overtravel of the hammer after seating of the magnetic plunger.

Referring to FIG. 3, there is shown a detail construction of the solenoid and clevis and plunger assembly. The solenoids are mounted in banks on respective magnet bars 20. A magnet bar, as shown in FIG. 3, comprises a bottom portion 21, top portion 22 and two side portions 23 and 24, all of magnetic iron. The solenoid plungers 11 enter through holes in the top member 22 of the magnet bar. These holes are lined with nonmagnetic wear-resisting material 34 which provides plunger guidance. Aligned with the holes in the top members are threaded holes in the bottom portion of the magnet bar by which threaded pole pieces 25 are supported and by which adjustment of the plunger travel is made. The pole pieces are made secure by means of locking nuts 26. The end member 23 is extended and shaped at the top portion of magnet bar 20 into a means for restricting the motion of the plunger.

The individual solenoids are mounted on uniformly spaced centers along the magnet bar as shown in FIG. 2. In the particular embodiment shown, the four magnet bars 20 are oriented in uniform angular increments around the hammer pivot centers and extend the length of the print line. The angular displacement 0 is shown in FIGS. 1 and 4. The magnet bars are offset from each other along the print line as shown in FIG. 2 in uniformly spaced steps so that the solenoids incorporated in each magnet bar actuate every plural integral numbered hammer, such as every fourth hammer shown in FIG. 2; that is, magnet bar No. 1 actuates hammers l, 5, 9, 15, etc.; magnet bar No. 2 actuates hammers 2, 6, l0, 14, etc.; magnet bar No. 3 actuates hammers 3, 7, ll, 15, etc.; magnet bar No. 4 actuates hammers 4, 8, 12,16, etc.

At their ends, the magnet bars 20 contain holes 27 for mounting the bars to pulley castings 28 in the proper orientation. This fabrication of similar magnet bar constructions permits economies in manufacturing.

Referring to FIG. 2 and FIG. 5, it should be noted that associated with each print position there is a small pivoted hammer 7. Each hammer is mounted in a guiding slot 29 which is formed or machined into the hammer bar 30. Each guiding slot is spaced a uniform distance centerline to centerline, thus corresponding to the printing column spacing. The number of hammers, therefore, is equal to the desired maximum number of characters required in a printed line.

The four magnet bars, together with the hammer-supporting bar and the belt guard, are attached at each end to a pulley support casting. The castings in turn support the pulleys upon which the print belt is located and driven, and provide attachment to the frame of the printer. The print actuation system, together with the print belt, thus become a unit which may be assembled, adjusted and tested prior to incorporation into the printer.

Referring to FIG. 1, the leftmost solenoid assembly illustrates the improved magnetic circuitry provided by this invention. This arrangement improves magnet efficiency and minimizes leakage field. It optimizes the transfer of energy from the traction or pulling magnet to the print hammer while providing for simplicity in assembly and adjustment. In the particular arrangement shown, a hammer-actuating signal supplied by the hammer drive circuit is applied over conductors 31 and 32 to the coil winding 33. As shown in FIG. 3, the solenoid coils are supported and located by engaging coil spool projections with counter bores concentric with the plunger and pole piece holes. The working airgap of the solenoid is located at the center of the coil windings. This minimizes magnetic leakage fields and improves magnetic efficiency. The magnetic field M established by the coil indicates the flow of magnetic flux in the direction of the arrows shown by the magnetic field lines M of FIG. 1 through its common top, bottom and side members 22, 21, 23 and 24 of the common magnet bar 20.

In the design of the hammer, an optimization of mass location for printing energy requirement and for low inertia permitted higher speed of operation. The hammer is able to perform the print operation and retract in a short and consistent time interval to produce uniform spacing of characters along the print line while avoiding interference with the adjacent type elements on the belt, spaced a short distance away.

The above mentioned results were obtained with the general configuration of the hammer shown in detail in FIG. 4 in association with the coil bank No. I. The center of percussion of the hammer is located as close to the impact point of the hammer as practicable. By so arranging, a minimum of reaction in the pivot area can be achieved upon impact, thus reducing the potential wear considerably.

Particular attention should be given the curved hammer slot shown in FIG. 4 of the hammer. This slot is designed to serve a unique, two-fold purpose. It provides a means of easy assembly and disassembly of the associated clevis assembly with respect to the hammer. In addition, during the firing of any hammer, it provides a means of overtravel of the hammer in what is termed its free-flight" condition. Further reference will be made later in the description of a typical printing cycle.

As previously mentioned, the hammers differ from one another only in the angular orientation of the curved slot area. The angular orientation of the curved slots on the hammers corresponds and aligns with the angular orientation of the four coil bank assemblies as shown by the angular displacement 0 and corresponding hammer positions A, B, C and D.

The front faces of all the hammers are set in line by an adjustable back damper member and stop 15. All the hammers are held in a rest position against the damper member with individual coil springs 16.

In the course of printing a particular character on a page, the following sequence of the mechanical events takes place. The type-carrying belt which is rotating transversely across the machine presents the individually mounted characters passing at high speeds, in line, and in front of a row of print hammers. By means of the clevis and plunger assemblies, each individual print hammer is connected to its associated solenoid coil. When the predetermined character (selected through electronic means) approaches the desired print column, the solenoid associated with that column is actuated. This actuation pulls the plunger and clevis assembly, closing the preset airgap between mating faces of plunger and pole piece. The action of closing the airgap consequently moves the print hammer to a point wherein the hammer faces on the same line with the rear surface of the type element and imparts sufficient kinetic energy to the hammer to perform the print action. At this point, the accelerating force due to the electromagnets ceases. Since the hammer at this point is traveling at an extremely high speed, it possesses momentum which tends to carry it beyond the rear surface of the type element. The curved slot in the hammer which cooperates with the clevis allows the hammer to continue to travel forward toward the platen 6 in what is termed a free-flight condition.

The hammer thus strikes the rear surface of the preselected character and causes it to move forward, with the hammer in its free-flight condition, until it strikes the ribbon and paper. After performing the print action, the hammer rebounds, avoiding the next character approaching along the print line.

As mentioned above, the solenoid is energized slightly ahead of the approaching character so that they impact the paper, properly registered, in the desired print column. In a particular embodiment, the above mentioned sequence of events, from coil activation to character strike on paper, takes approximately 1.3 milliseconds time span.

While all this invention has been described with respect to a preferred embodiment and several illustrative examples thereof, it is to be clearly understood by those skilled in the art that the invention is not limited thereto. The invention is intended to be bounded only by .the limits of the appended claims.

We claim:

1. In a printing apparatus of the kind type comprising a character type carrier in the form of an endless belt, said belt being horizontally displaceable in parallel to a text line to be printed on a printing surface, type-carrying elements being disposed adjacent to each other in said belt and adapted for individual movement transverse to the longitudinal extension thereof, type-actuating means stationary in said apparatus and adapted for selectively moving at least one, at a time, of said type-carrying elements in the aforesaid manner, so as to effect printing of said text line, said type-actuating means comprising a shaft, a plurality of hammers pivotally mounted side by side on said shaft, a plurality of magnetic bars extending the full length of the print line and oriented in uniform angular increments around the hammer pivot centers, said magnetic bars comprising top and bottom members and side members of magnetic material, a plurality of solenoids associated with each magnetic bar and supported thereon, in uniformly spaced-apart location, each solenoid comprising a winding, plunger and pole piece, the solenoid plungers entering through holes in the top member of the associated bar, pole pieces entering through holes in the bottom memberof the associated bar and adjustably threaded thereto and in line with the holes in the top member, the magnet bars being uniformly offset from one another along the print line so that the solenoids incorporated in each magnet bar actuate every plural integral numbered hammer along the print line, the coils being located between the top and bottom members, means for selectively energizing each of said coils to provide a magnetic flux flowing between its common top and bottom members through its common side members and in the same direction through its pole piece and plunger, said coil responsive to being energized to move the plunger toward the pole piece, individual clevis assemblies responsive to plunger movement for driving its respective hammer about said shaft each of said hammers adapted to strike one end of the type-carrying element passing before it when the solenoid associated with that particular hammer is energized.

2. An arrangement according to claim 1 comprising means for selectively energizing a predetermined number of said solenoids in determined positions independently of the other solenoids.

3. An arrangement by which printable characters transported across a page may be printed comprising magnetically actuated hammers aligned along a print line comprising four banks of electrically driven solenoids, each solenoid providing actuation for a respective print hammer, individual hammers at each print position mounted on a single hammer pivot bar, clevis assemblies connecting each hammer to a plunger associated with its respective solenoid, the solenoids of each bank being mounted on uniformly spaced centers along a respective magnet bar of magnetic iron, the four magnet bars being uniformly oriented in uniform angular increments around the hammer pivot centers and extending the length of the print line, the magnet bars being offset from each other along the print line in fixed displacements so that the solenoids incorporated in each magnet bar actuate every fourth hammer, each magnet bar providing a common magnetic return path for all of the solenoids incorporated in it and acting as a beam to support actuation forces of the solenoid, said magnetic bars comprising top and bottom and side members, said solenoid plungers entering through holes in the top member of the associated magnetic bar, said hole being lined with nonmagnetic, wear-resisting material which provides plunger guiding, aligned with the holes in the top member are threaded holes in the bottom member of the magnetic bar, pole pieces threaded in each bottom member hole, each of said solenoids comprising coils supported and located concentric with the plunger and pole piece holes, the working airgap of solenoids being located at the center of the coil windings.

4. An arrangement by which printable characters transported across a print line may be printed at desired print column positions along said line comprising respective hammers located at each print column position, means for actuating each of said hammers to pivot about a common pivot axis and cause printing of said printable characters at respective column positions comprising a plurality of banks of electrically driven solenoids, each solenoid providing actuation for a respective hammer, a plurality of magnetic bars, each of said magnetic bars associated with a respective bank, extending the full length of the print line and differently angularly oriented around said hammer pivot axis, said magnetic bars comprising top and bottom members and side members of magnetic material, a bank of solenoids associated with each magnetic bar and supported thereon in spaced-apart locations, each solenoid comprising at least a coil plunger and pole piece, the solenoid plungers entering through holes in the top member of the associated bar, pole pieces entering through.

holes in the bottom member of the associated bar and aligned with respective holes in the top member, the coils being located between the top and bottom members, and means for selectively energizing each of said coils to provide a magnetic flux path between its associated common top and bottom members through its common side member and its associated coil.

5. An arrangement by which printable characters transported across a print line may be printed at desired positions along said print line comprising a plurality of hammers aligned along said pring line, a plurality of banks of electrically driven solenoids, each solenoid comprising a respective magnetic circuit for providing actuation for an associated, respective hammer, a plurality of magnetic bars, each of said magnetic bars associated with a respectively different bank of solenoids and extending the full length of the print line and angularly oriented with respect to the hammers, each of said magnetic bars providing a common magnetic return path for all of the magnetic circuits of the associated bank of solenoids and providing a common base for the delivery of the actuation forces by such solenoids.

6. An arrangement according to claim 5 wherein the sole noids associated with each magnetic bar are located along said magnetic bar and oriented with respect to associated hammers to actuate only nonadjacent hammers.

7. An arrangement according to claim 6 wherein the magnetic circuit of each solenoid comprises a respective magnetic series circuit of a plunger, airgap and pole piece and a return path comprising said magnetic bar, said plunger responsive to energization of said magnetic circuit for actuating a respective hammer.

8. An arrangement according to claim 7 wherein said series circuit is substantially surrounded by the magnetic bar.

9. An arrangement according to claim 7 wherein each of said solenoids further comprises a coil with the working airgap being located substantially at the center of the coil to minimize magnetic interaction with adjacent solenoids.

10. An arrangement by which printable characters transported across a print line may -be printed at desired print column positions along said line comprising respective hammers located at each print column position, means for actuating each of said hammers to pivot about a pivot axis and cause printing of said printable characters at respective column positions comprising a plurality of rows of electrically driven solenoids, a respective magnet bar associated with each of said rows of solenoids, means for supporting the solenoids of each row in spaced-apart location on an associated one of said magnet bars for actuation of only nonadjacent hammers aligned along said print line, each of the magnet bars being oriented at a different angle around the pivot axis of the associated hammers and extending the length of the print line, means for energizing each solenoid to provide actuation for a respective hammer about its pivot center, and means for energizing the solenoids incorporated in each magnet bar to actuate every plural integral numbered hammer along said print line.

11. An arrangement according to claim 10 wherein each magnet bar provides a common magnetic return path for all of the solenoids incorporated in it and provides a common base for the delivery of the actuation forces of its solenoids.

12. An arrangement according to claim 11 wherein said magnetic bars comprise top and bottom and side members enclosing said solenoids, said solenoids comprise plungers, the top member of each magnetic bar dimensioned to include openings for permitting plunger movement therethrough and in magnetic circuit therewith, aligned with the holes in the top member are holes in the bottom member of the magnetic bar, pole pieces located in the bottom member holes of the associated magnetic bar and in magnetic circuit therewith, said solenoid comprising coils associated with respective ones of the plungers and pole pieces, the working airgap of solenoids being located substantially at the center of the coil windings.

13. An arrangement by which print characters transported across a print line may print at desired print column positions along said line comprising respective hammers located at each print column position, means for actuating each of said hammers to pivot about a common pivot axis and cause printing by said print characters at a respective column position comprising a plurality of rows of electrically driven solenoids, a respective magnetic bar associated with each of said rows, means for supporting the solenoids of each row in spacedapart location along an associated one of said magnetic bars for actuation of only those associated hammers whose numbering along a print line is established by the progression 1 (n l) 2n 1 +...where n is the value of said plurality of rows, each of said magnetic bars being oriented at a different angle around the pivot axis of the associated hammers and extending the length of the print line, and means for energizing the solenoids incorporated in each magnetic bar to simultaneously actuate more than one of the hammers associated with such magnetic bar. 

1. In a printing apparatus of the kind type comprising a character type carrier in the form of an endless belt, said belt being horizontally displaceable in parallel to a text line to be printed on a printing surface, type-carrying elements being disposed adjacent to each other in said belt and adapted for individual movement transverse to the longitudinal extension thereof, type-actuating means stationary in said apparatus and adapted for selectively moving at least one, at a time, of said type-carrying elements in the aforesaid manner, so as to effect printing of said text line, said type-actuating means comprising a shaft, a plurality of hammers pivotally mounted side by side on said shaft, a plurality of magnetic bars extending the full length of the print line and oriented in uniform angular increments around the hammer pivot centers, said magnetic bars comprising top and bottom members and side members of magnetic material, a plurality of solenoids associated with each magnetic bar and supported thereon, in uniformly spaced-apart location, each solenoid comprising a winding, plunger and pole piece, the solenoid plungers entering through holes in the top member of the associated bar, pole pieces entering through holes in the bottom member of the associated bar and adjustably threaded thereto and in line with the holes in the top member, the magnet bars being uniformly offset from one another along the print line so that the solenoids incorporated in each magnet bar actuate every plural integral numbered hammer along the print line, the coils being located between the top and bottom members, means for selectively energizing each of said coils to provide a magnetic flux flowing between its common top and bottom members through its common side members and in the same direction through its pole piece and plunger, said coil responsive to being energized to move the plunger toward the pole piece, individual clevis assemblies responsive to plunger movement for driving its respective hammer about said shaft each of said hammers adapted to strike one end of the type-carrying element passing before it when the solenoid associated with that particular hammer is energized.
 2. An arrangement according to claim 1 comprising means for selectively energizing a predetermined number of said solenoids in determined positions independently of the other solenoids.
 3. An arrangement by which printable characters transported across a page may be printed comprising magnetically actuated hammers aligned along a print line comprising four banks of electrically driven solenoids, each solenoid providing actuation for a respective print hammer, individual hammers at each print position mounted on a single hammer pivot bar, clevis assemblies connecting each hammer to a plunger associated with its respective solenoid, the solenoids of each bank being mounted on uniformly spaced centers along a respective magnet bar of magnetic iron, the four magnet bars being uniformly oriented in uniform angular increments around the hammer pivot centers and extending the length of the print line, the magnet bars being offset from each other along the print line in fixed displacements so that the solenoids incorporated in each magnet bar actuate every fourth hammer, each magnet bar providing a common magnetic return path for all of the solenoids incorporated in it and acting as a beam to support actuation forces of the solenoid, said magnetic bars comprising top and bottom and side members, said solenoid plungers entering through holes in the top member of the associated magnetic bar, said hole being lined with nonmagnetic, wear-resisting material which provides plunger guiding, aligned with the holes in the top member are threaded holes in the bottom member of the magnetic bar, pole pieces threaded in each bottom member hole, each of said solenoids comprising coils supported and located concentric with the plunger and pole piece holes, the working airgap of solenoids being located at the center of the coil windings.
 4. An arrangement by which printable characters transported across a print line may be printed at desired print column positions along said line comprising respective hammers located at each print column position, means for actuating each of said hammers to pivot about a common pivot axis and cause printing of said printable characters at respective column positions comprising a plurality of banks of electrically driven solenoids, each solenoid providing actuation for a respective hammer, a plurality of magnetic bars, each of said magnetic bars associated with a respective bank, extending the full length of the print line and differently angularly oriented around said hammer pivot axis, said magnetic bars comprising top and bottom members and side members of magnetic material, a bank of solenoids associated with each magnetic bar and supported thereon in spaced-apart locations, each solenoid comprising at least a coil plunger and pole piece, the solenoid plungers entering through holes in the top member of the associated bar, pole pieces entering through holes in the bottom member of the associated bar and aligned with respective holes in the top member, the coils being located between the top and bottom members, and means for selectively energizing each of said coils to provide a magnetic flux path between its associated common top and bottom members through its common side member and its associated coil.
 5. An arrangement by which printable characters transported across a print line may be printed at desired positions along said print line comprising a plurality of hammers aligned along said pring line, a plurality of banks of electrically driven solenoids, each solenoid comprising a respective magnetic circuit for providing actuation for an associated, respective hammer, a plurality of magnetic bars, each of said magnetic bars associated with a respectively different bank of solenoids and extending the full length of the print line and angularly oriented with respect to the hammers, each of said magnetic bars providing a common magnetic return path for all of the magnetic circuits of the associated bank of solenoids and providing a common base for the delivery of the actuation forces by such solenoids.
 6. An arrangement according to claim 5 wherein the solenoids associated with each magnetic bar are located along said magnetic bar and oriented wiTh respect to associated hammers to actuate only nonadjacent hammers.
 7. An arrangement according to claim 6 wherein the magnetic circuit of each solenoid comprises a respective magnetic series circuit of a plunger, airgap and pole piece and a return path comprising said magnetic bar, said plunger responsive to energization of said magnetic circuit for actuating a respective hammer.
 8. An arrangement according to claim 7 wherein said series circuit is substantially surrounded by the magnetic bar.
 9. An arrangement according to claim 7 wherein each of said solenoids further comprises a coil with the working airgap being located substantially at the center of the coil to minimize magnetic interaction with adjacent solenoids.
 10. An arrangement by which printable characters transported across a print line may be printed at desired print column positions along said line comprising respective hammers located at each print column position, means for actuating each of said hammers to pivot about a pivot axis and cause printing of said printable characters at respective column positions comprising a plurality of rows of electrically driven solenoids, a respective magnet bar associated with each of said rows of solenoids, means for supporting the solenoids of each row in spaced-apart location on an associated one of said magnet bars for actuation of only nonadjacent hammers aligned along said print line, each of the magnet bars being oriented at a different angle around the pivot axis of the associated hammers and extending the length of the print line, means for energizing each solenoid to provide actuation for a respective hammer about its pivot center, and means for energizing the solenoids incorporated in each magnet bar to actuate every plural integral numbered hammer along said print line.
 11. An arrangement according to claim 10 wherein each magnet bar provides a common magnetic return path for all of the solenoids incorporated in it and provides a common base for the delivery of the actuation forces of its solenoids.
 12. An arrangement according to claim 11 wherein said magnetic bars comprise top and bottom and side members enclosing said solenoids, said solenoids comprise plungers, the top member of each magnetic bar dimensioned to include openings for permitting plunger movement therethrough and in magnetic circuit therewith, aligned with the holes in the top member are holes in the bottom member of the magnetic bar, pole pieces located in the bottom member holes of the associated magnetic bar and in magnetic circuit therewith, said solenoid comprising coils associated with respective ones of the plungers and pole pieces, the working airgap of solenoids being located substantially at the center of the coil windings.
 13. An arrangement by which print characters transported across a print line may print at desired print column positions along said line comprising respective hammers located at each print column position, means for actuating each of said hammers to pivot about a common pivot axis and cause printing by said print characters at a respective column position comprising a plurality of rows of electrically driven solenoids, a respective magnetic bar associated with each of said rows, means for supporting the solenoids of each row in spaced-apart location along an associated one of said magnetic bars for actuation of only those associated hammers whose numbering along a print line is established by the progression 1 + (n + 1) + 2n + 1 +...where n is the value of said plurality of rows, each of said magnetic bars being oriented at a different angle around the pivot axis of the associated hammers and extending the length of the print line, and means for energizing the solenoids incorporated in each magnetic bar to simultaneously actuate more than one of the hammers associated with such magnetic bar. 